Siemens Medical Solutions Usa, Inc.

Manojeet Bhattacharya

Xinhong Ding

For dead time determination for a gamma camera or other detector, a long-lived point source of emissions is positioned so that the gamma camera detects the emissions from the source while also being used to detect emissions from the patient. The long-lived point source, in the scan time, acts as a fixed frequency source of emissions, allowing for dead time correction measurements that include the crystal detector effects.

Gamma camera dead time determination in real time using long lived radioisotopes

For dose calibration () in functional imaging, different precision sources () for a same long-lived isotope are used to calibrate, avoiding having to ship one source from one location to another location. A ratio of sensitivities of a gas ion chamber-based dose calibrator () at a reference laboratory to the precision source () of the long-lived isotope to a source () with an isotope to be used for imaging is found. At the clinical site (e.g., radio-pharmacy or functional imaging facility), a measure () of the sensitivity of a local gas ion chamber-based dose calibrator () to the other source () with the long-lived isotope and the ratio from the remote gas ion chamber-based dose calibrator () are used to determine sensitivity of the local gas ion chamber-based dose calibrator () to the isotope of the radiopharmaceutical (). The bias and corresponding dose for the radiopharmaceutical () to be used for imaging a patient are based on activity for the radiopharmaceutical () as calibrated to account for the sensitivity of the local gas ion chamber-based dose calibrator () to the isotope of the radiopharmaceutical ().

Calibration bias reduction in a pressurized gas ion chamber-based dose calibrator

During calibration of a SPECT system, system-specific sensitivities and cross-calibration factors for multiple isotopes for correcting for dose are determined for various combinations of options, including the option of which specific well counter with which to measure the dose. The options may include selected energy windows for isotopes with multiple energy windows. This arrangement allows for custom-specified isotopes not included in standard listings. For use with a particular patient, the cross-calibration factor for the well counter used to measure the dosage for the patient is accessed and used for dose correction. More accurate quantitative functional information may result from the corrected dose. The cross-calibration may be more easily implemented despite the options using the sensitivities and cross-calibrations provided for various combinations.

Flexible application of cross-calibration for quantitative functional imaging

A detector of a gamma camera is configured such that a radioactive point source is positioned within a field of view at a fixed distance from the detector. A predetermined number of gamma photons emitted by the point source and passed through a collimator are acquired. A system-specific planar sensitivity is computed for a combination of the collimator and detector using the number of gamma photons acquired, a time duration of the acquisition, and precalibrated radioactivity data of the point source corrected for decay that occurred after a precalibration time. A deviation of the computed system-specific planar sensitivity from a class standard sensitivity value for a combination of the radioactive point source, the collimator, and the detector is computed. A class standard sensitivity value for a combination of a radiopharmaceutical, the collimator, and the detector is scaled by the computed deviation, yielding a scaled system-specific sensitivity value for the radiopharmaceutical.

Method and apparatus for sensitivity calibration

Cross-calibration is provided for functional imaging. In PET or SPECT, the inaccuracies from the dose and detector sensitivity may be reduced or removed in both activity concentration and uptake. By using measures from both the radiotracer for the patient and factory calibrated sources, the variability due to dose may be removed. In SPECT, a measurement of system specific sensitivity to a factory calibrated point source is used to improve the accuracy of uptake values, not just activity concentration.

Cross-calibration for quantitative functional imaging

For dose calibration in functional imaging, an amount of bias in a dose calibrator measurement of activity is determined using a spectroscopic detector. The bias may then be used to correct dose values for the same isotope used to determine a factory-based sensitivity of the functional imaging system. When local functional imaging systems are calibrated, any difference in sensitivity from the factory measured sensitivity may be due to local dose calibrator bias, so the difference in sensitivity is used to determine a local correction.

Isotope specific calibration of a dose calibrator for quantitative functional imaging

For calibration () for quantitative SPECT, a multiple energy emission source () is used for calibration. The planar sensitivities and/or uniformities are determined at different emission energies based on detections from the multiple energy emission source. For estimating () the activity concentration, sensitivities and/or uniformities based on measures () at different emission energies increase accuracy. The multiple energy emission source () may alternatively or additionally be used to calibrate () a dose calibrator ().

Calibrating in single photon emission computed tomography with multi-emission energies

For dead time compensation, a point source with a same radioisotope as used for the radiopharmaceutical is positioned by the detector. Counts from the point source without the patient and with the patient are used to correct the system or detector sensitivity. Reconstruction is performed with the sensitivity normalized for count rate, compensating for the dead time and spectral broadening.

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Manojeet Bhattacharya